"I have always said that Danny pulled the trigger but he's not the only one with my son's blood on his hands," she said.

"G4S is the third largest private sector employer in the world. It's time these rich and powerful organisations were properly accountable and that should start with an apology to all of us, to Paul's family.

"We've never had an apology after five and a half years."

Fitzsimons, a former soldier in the Parachute Regiment, had been dismissed from the Army and was on the run for a string of offences when the security firm took him on without vetting him properly.

A steroid user, described as violent and unpredictable, especially when drunk, Fitzsimons held extreme racist views, and according to one doctor's assessment only showed any excitement when talking about involvement in football hooliganism and firing guns.

In pages of writings recovered by police from his home he had written: "I have lived a life of violence. Any chance I have to do someone I will take it."

He was being dealt with by the Probation Service after offences of assaults, robbery and possession of ammunition but there were "significant missed opportunities" to properly assess and supervise him, the inquest heard.

While on bail he got the job with G4S, flew out to Baghdad, was issued with weapons, got drunk and shot dead his two colleagues at a base, less than 12 hours after arriving in the Green Zone of the Iraqi capital.

Fitzsimons, 34, had got into "banter" with Mr McGuigan, a former Royal Marine from Peebles, Scotland, and later claimed he killed the two men in self defence after they attacked him.

But no defence injuries were discovered on either man and Fitzsimons was later found guilty of both murders by a court in Iraq.

Each victim was shot three times with a Glock 9mm pistol - Mr McGuigan, a father of two, shot twice in the chest and once at point blank range in the mouth. Fitzsimons also shot and injured an Iraqi security guard before his arrest.

The inquest into Mr McGuigan's death, which first began last September at Stockport Coroner's Court, heard mistakes were made by the Probation Service in dealing with Fitzsimons before he jumped bail and went to Iraq and questions were raised over G4S's role in recruiting, vetting and deploying him to Iraq in 2009.

It was a "defining moment for the global security industry" at the time, the inquest heard, with security firms under pressure to recruit ex-forces personnel given the dangerous conditions in post-invasion Iraq.

Fitzsimons was deployed to Iraq without up-to-date references, with no criminal records bureau check and with a forged medical certificate.

During the inquest G4S staff accepted Fitzsimons should not have been sent to Iraq.

A fellow security guard who had come across Fitzsimons previously, saw his posts on Facebook talking of his forthcoming deployment, along with writings of a sexually violent nature, and sent emails from Afghanistan to G4S warning them not to employ him in such a volatile environment, but the emails were never received.

Joanne Kearsley, area coroner for South Manchester, rejected Fitzsimons' claims he suffered post traumatic stress disorder after serving with the Paras in the Balkans War.

Delivering her 91-page narrative verdict, Ms Kearsley added: "There were missed opportunities and failings by the Probation Service to manage the escalating offending behaviour and risk presented by the offender prior to his deployment abroad. In addition G4S did not ensure that he was adequately vetted prior to being deployed to work as a close protection officer."

Ms Kearsley said G4S is an international company but at the time of employing Fitzsimons, and hundreds of others for work in the Middle East, the human resources team consisted of three people, with two people doing all vetting of recruits and the firm struggling to operate in an industry that was unregulated at the time.

Mr McGuigan, described as a "solid, professional and dependable man," had been living in Tameside at the time of his death and had previously worked as a bodyguard for ex-Beatle George Harrison.

He had one son, Reece McGuigan, 10, from a previous relationship and his fiancee Nicola Prestage, 37, was pregnant with his daughter, Elsie-mai, when he was shot by Fitzsimons.

Outside court Ms Prestage said: "He's nothing but a psychopath and in his own words was bloodthirsty to kill again."

In a statement G4S said: "The death of Paul McGuigan came as a profound shock to G4S. Paul McGuigan was a son, a partner, a father and a colleague, and G4S extends its sincerest sympathies to his family for the anguish they have suffered as a result of his loss.

"Industry standards for the recruitment of private security operators in high-threat environments have advanced significantly in the years following this tragic incident. G4S has played a key role in promoting those changes."

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